Controllable Pitch Propeller
Canada is not exactly known for having produced
several ground-breaking
inventions or discoveries in her time. However, the
period of rapid
technological advancement that she incurred during the third
period of the
history of engineering in Canada brought with it several
important engineering
inventions which had their roots in Canada. The
creation of the controllable
pitch propeller was one such invention which was
perfected in Canada and was so
successful that this primarily Canadian
development spread throughout the world.
Wallace Rupert Turnball lived in
Rothesay and it was there that he carried out
his experiments in aeronautical
theory beginning in 1902. His specialty was that
of dihedrals which he
studied in a wind-tunnel. He looked at water borne
hydroplanes propelled by
motor-driven airscrews. An airscrew the Great Britain
term for a propeller. A
standard propeller consists of anywhere from two to four
blades each a
section of a helix, the geometric form of a screw thread, hence
the term
"airscrew." The first plane had two air-screws on each side whereas
the
second one had only one, more highly efficient propeller located at the
rear
end of craft, near the pilot’s seat. However, both had an uneven torque
of
engine that was in fact destructive to the efforts of the propeller.
Turnball
experimented with all different types of air-screws; some with a 30"
gauge
track that were 300’ long for truck. With each air-screw he tested,
he
recorded the propeller thrust, rpm and the forward speed. What determines
the
forward speed is the distance that a propeller will move in the
forward
direction when the shaft of the propeller is rotated 360o. Assuming
that there
is no slippage, this distance is termed the geometric pitch. The
propellers that
Turnball tested had diameters ranging from 1.5’ up to
3.5’, all different
dimensions and shapes. Upon his return to Rothesay in
1918, after the war, he
dove into his research and experimentation on a
possible controllable pitch
propeller, an idea that he had been developing
since the autumn of 1916. He ran
several tests using rotating electric motor
apparatus in order to spin the
blades of his propeller. The finished product
was a propeller whose pitch can be
adjusted by the pilot, at different
angles, during flight giving the pilot the
ability to command the optimal
combination of torque and speed for the situation
at any given moment from
his aircraft. By means of a small electric motor
mounted just in front of the
propeller, the pitch of the propeller itself could
eventually be adjusted
which makes for more efficient take-offs and regular
flight than what would
be achieved with an everyday "fixed blade" propeller
incapable of any pitch
change. Under the supervision of both the Ontario
government and the Canadian
Air Force, a ground test was run in 1923 on Avro
aircraft at Camp Borden,
Ontario only to conclude that more research and
experimentation was
necessary. Four years later, on June 6, 1927, again at Camp
Borden on
Avro Biplane, Flight Lieutenant G.G. Brookes took Turnball’s
controllable
pitch propeller for it’s first air test. Funding was granted
immediately to
perfect the invention it was such a success. The news of the
Canadian
invention spread rapidly. Turnball wrote a treatise based on his
discoveries
and new found technology called "The Efficiency of Aerial
Propellers"
which was published in the Scientific American on April 3, 1909.
His
second and third publications on the subject were entitled "Laws
of
Air-Screws" and appeared in The Aeronautical Journal, in the October
1910 and
January 1911 issues. For his studies and discoveries, Turnball
was awarded the
Bronze Medal of Royal Aeronautical Society and was, in
addition, elected a
"Fellow." Come 1914, Turnball had published several
scientific articles and
found himself one of the world’s authorities on the
subject. He sold the
patents to the controllable pitch propeller in December
of 1929. The Curtiss
Wright Corporation won the American rights and the
Bristol Aeroplane Company,
the English rights. In 1935, the Norseman, the
most highly successful bush plane
in the world at the time, was designed in
Canada by Robert Noorduyn, an aviation
engineer trained in Holland. The
Norseman quickly caught the attention of the
entire world due to the
effectiveness of its design. It had a large capacity for
cargo, flexible
take-off and landing capabilities, ability to withstand harsh
weather, can be
easily flown in either day or night and is capable of flying
great distances.
Noorduyn’s Norseman, which utilized Turnbull’s controllable
pitch propeller,
was adopted around the world by countries that required short
take off and
landing (STOL) planes for their own reasons, most of which involved
mining,
lumbering and exploring isolated expanses of land which could not
otherwise
be reached quite as easily. W.R. Turnball’s invention of the
controllable
pitch propeller was clearly one of the most successful Canadian
innovations
in terms of world recognition. Once perfected, it was quickly bought
up by
major aircraft manufacturing companies around the world and mass produced
to
fulfill the global demand, at the time, for such a development in
technology.